1. Field of the Invention
The present invention relates to surgical implants, and in particular to a prosthetic device for replacing injured ligamentous structures.
2. Description of the Related Art
Fibrous connective tissues (e.g., ligaments and tendons) provide essential support and stability to the musculoskeletal system. Damage to or loss of these tissues can result in disabling permanent injury. Unfortunately, because of the large and repeated stresses to which they are subjected even by routine activity, their replacement or reconstruction is particularly problematic. Prostheses for fibrous connective tissues must not only retain functional integrity under heavy mechanical burdens, but also withstand the body's natural degradative processes while maintaining biological and physical compatibility with surrounding tissue; in addition, they should facilitate immediate joint motion following surgery and a minimal period of activity restriction. This highly demanding combination of requirements has heretofore limited the success of prostheses fabricated from synthetic material, and surgeons therefore often resort to autogenous tissue grafts for augmentation or replacement of damaged fibrous connective tissues. Prior artificial devices have either failed mechanically in situ or caused unintended damage to surrounding tissue by abrasive wear, fragmentation, debris formation, joint effusion, joint laxity, restricted joint motion, contraction and/or calcification.
An attempt to surmount these difficulties using a combination of absorbable and nonabsorbable prosthetic components is described in U.S. Pat. No. 4,942,875. This reference describes repair devices consisting of mixed fiber bundles woven, braided or knitted together. While such devices may offer biological compatibility with surrounding tissues, their necessarily rough surfaces have been known to cause substantial abrasion damage to surrounding tissues over time as a consequence of the patient's post-operative activity. Moreover, like other prior approaches, the '875 devices make no mechanical provision for the multicentric axes of rotation encountered anatomically. One immediate result is loss of joint motion; but over time, the mechanical stresses imposed by natural joint action can result in weakening and, ultimately, fragmentation and breakage of the prosthetic fibers, since these are designed to accommodate only longitudinal forces. Indeed, even purely longitudinal stresses can ultimately cause failure of such devices if localized to particular longitudinal fibers.
Finally, prior devices such as that disclosed in the '875 patent do not support significant vascular ingrowth or deep tissue permeation, particularly in the case of relatively thick prostheses. Such tissue growth is essential both to integration of a prosthesis within its surrounding tissue enviromnent, as well as to the regeneration of natural fibrous connective tissue to enhance the performance of the prosthesis itself.